1. Field of the Invention
The present invention relates to a detection method, and more particularly, to a method for detecting whether vertical deviation of an optical disc occurs while the optical disc is spinning in an optical disc player or an optical disc writer.
2. Description of the Prior Art
Vertical deviation refers to the wobbling of an optical disc, along the perpendicular direction of the spinning level that the optical disc is spinning on, while the optical disc is spinning in the optical disc player or optical disc writer. Vertical deviation causes data reading to be unstable, writing quality to be inconsistent, and noise to be produced while the machine is operating.
Vertical deviation usually results from poor quality of the optical disc; this kind of undesired disc is called vertical deviation disc. In the field of disc manufacturing, there are many related technologies to prevent vertical deviation discs from being manufactured. Besides, many industrial instruments are used to detect whether an optical disc is a vertical deviation disc.
However, consumers may encounter a vertical deviation disc while using an optical disc player or optical disc writer. The reason could be attributed to inadequate quality management of the disc manufacturer or the imbalanced mass of the optical disc caused by damage after the optical disc left the factory. Because the prevention of vertical deviation is considered to be the responsibility of the disc manufacturers, optical disc players or optical disc writers generally don't include the detection method for detecting whether the optical disc is a vertical deviation disc.
Besides, an optical disc player or optical disc writer can read some of the vertical deviation discs. In the prior art, an optical disc player or optical disc writer is designed to be able to keep the focus length from the optical disc in order to read data, the so-called focus. Therefore, although the vertical deviation disc wobbles along the perpendicular direction of the spinning level, the pickup head can follow the wobbling of the optical disc and keep focusing to read data.
Because the prevention of vertical deviation of an optical disc is considered to be the responsibility of the disc manufacturers, and because some of the vertical deviation discs are still readable, manufacturers of optical disc player and optical disc writer usually ignore the problem of vertical deviation. Users of optical disc players and optical disc writers depend on the abnormal noise made while the optical disc is spinning in the machine or on inconsistent quality of reading or writing to determine whether the optical disc presently used is a vertical deviation disc. Therefore, the conventional optical disc player and optical disc writer lack a vertical deviation disc detection method.